I beg to differ, @davidgo. The references you are quoting are a tad obsolete: while crontab does work, /etc/rc.local does not on systemd distros like Arch Linux. By referring to them, we might be sending Demetri on a wild goose chase. Some updating, at times, needs to be done.
–
MariusMatutiaeDec 8 '13 at 7:41

3 Answers
3

If you are on Debian-derived distros, there are at least two proper places, /etc/rc.local and crontab. You may invoke crontab as root,

crontab -e

and then insert this line

@reboot /home/my_name/bin/my_command

where my_command is an executable file (chmod 755 my_command).

Alternatively, you may place a line like this

/home/my_name/bin/my_command

in /etc/rc.local, and this will be executed last. In any case, pls do remember you are using root environment, not yours. Also for this reason, it is best to use absolute paths.

If you are on a systemd distro (Arch Linux, Fedora 19,...) the first option (crontab) is still valid, while the second one (/etc/rc.local) does not exist any longer. In this case, you should learn how to start a service to be run by systemctl, but this may be more than you bargained for with your simple question.

Can you confirm this for Fedora ? My searching tells me that rc.local will still run if it exists and is executable, but is not set up by default. I perceived troubling ramifications if rc.local does not run ! (I could only find references for this for Fedora 18 - forums.fedoraforum.org/showthread.php?t=291889)
–
davidgoDec 8 '13 at 7:43

Please note that startup, as far as @reboot is concerned, is the time when the cron(8) daemon startup. In particular, it may be before some system daemons, or other facilities, were startup. This is due to the boot order sequence of the machine.

This is far from being the only way to run something at boot time, but it's an alternative.

This question shows a lack of even basic research.
Pretty much all variants of Linux (going back a long, long time) have a file /etc/rc.local which runs on startup - you can just add the command to it.

That said, you don't even need to do that. The "correct" way would be to modify / add the line kernel.sysrq = 1 into /etc/sysctl.conf